Ubuntu Manpage: snmpusm - creates and maintains SNMPv3 users on a network entity

Provided by: snmp_5.8+dfsg-2ubuntu2.9_amd64

NAME

       snmpusm - creates and maintains SNMPv3 users on a network entity

SYNOPSIS

       snmpusm [COMMON OPTIONS] [-Cw] AGENT create USER [CLONEFROM-USER]
       snmpusm [COMMON OPTIONS] AGENT delete USER
       snmpusm [COMMON OPTIONS] AGENT cloneFrom USER CLONEFROM-USER
       snmpusm [COMMON OPTIONS] [-Ca] [-Cx] AGENT passwd OLD-PASSPHRASE NEW-PASSPHRASE [USER]
       snmpusm [COMMON OPTIONS] <-Ca | -Cx> -Ck AGENT passwd OLD-KEY-OR-PASSPHRASE NEW-KEY-OR-PASSPHRASE [USER]
       snmpusm [COMMON OPTIONS] [-Ca] [-Cx] AGENT changekey [USER]

DESCRIPTION

       snmpusm  is  an  SNMP application that can be used to do simple maintenance on the users known to an SNMP
       agent, by manipulating the agent's User-based Security Module (USM) table.  The user needs  write  access
       to the usmUserTable MIB table.  This tool can be used to create, delete, clone, and change the passphrase
       of users configured on a running SNMP agent.

OPTIONS

       Common options for all snmpusm commands:

       -CE ENGINE-ID
              Set usmUserEngineID to be used as part of the index of the usmUserTable.  Default is  to  use  the
              contextEngineID (set via -E or probed) as the usmUserEngineID.

       -Cp STRING
              Set the usmUserPublic value of the (new) user to the specified STRING.

       Options for the passwd and changekey commands:

       -Ca    Change the authentication key.

       -Cx    Change the privacy key.

       -Ck    Allows  one  to use localized key (must start with 0x) instead of passphrase.  When this option is
              used, either the -Ca or -Cx option (but not both) must also be used.

CREATING USERS

An unauthenticated SNMPv3 user can be created using the command

snmpusm [COMMON OPTIONS] AGENT create USER

This constructs an (inactive) entry in the usmUserTable, with no authentication or privacy settings. In
principle, this user should be useable for 'noAuthNoPriv' requests, but in practise the Net-SNMP agent
will not allow such an entry to be made active. The user can be created via the createAndWait operation
instead by using the -Ca flag. This will prevent the user from being marked as active in any agent until
explicitly activated later via the activate command.

In order to activate this entry, it is necessary to "clone" an existing user, using the command

snmpusm [COMMON OPTIONS] AGENT cloneFrom USER CLONEFROM-USER

The USER entry then inherits the same authentication and privacy settings (including pass phrases) as the
CLONEFROM user.

These two steps can be combined into one, by using the command

snmpusm [COMMON OPTIONS] AGENT create USER CLONEFROM-USER

The two forms of the create sub-command require that the user being created does not already exist. The
cloneFrom sub-command requires that the user being cloned to does already exist.

Cloning is the only way to specify which authentication and privacy protocols to use for a given user,
and it is only possible to do this once. Subsequent attempts to reclone onto the same user will appear
to succeed, but will be silently ignored. This (somewhat unexpected) behaviour is mandated by the SNMPv3
USM specifications (RFC 3414). To change the authentication and privacy settings for a given user, it is
necessary to delete and recreate the user entry. This is not necessary for simply changing the pass
phrases (see below). This means that the agent must be initialized with at least one user for each
combination of authentication and privacy protocols. See the snmpd.conf(5) manual page for details of
the createUser configuration directive.

DELETING USERS

       A user can be deleted from the usmUserTable using the command

              snmpusm [COMMON OPTIONS] AGENT delete USER

CHANGING PASS PHRASES

User profiles contain private keys that are never transmitted over the wire in clear text (regardless of
whether the administration requests are encrypted or not). To change the secret key for a user, it is
necessary to specify the user's old passphrase as well as the new one. This uses the command

snmpusm [COMMON OPTIONS] [-Ca] [-Cx] AGENT passwd OLD-PASSPHRASE NEW-PASSPHRASE [USER]

After cloning a new user entry from the appropriate template, you should immediately change the new
user's passphrase.

If USER is not specified, this command will change the passphrase of the (SNMPv3) user issuing the
command. If the -Ca or -Cx options are specified, then only the authentication or privacy keys are
changed. If these options are not specified, then both the authentication and privacy keys are changed.

snmpusm [COMMON OPTIONS] [-Ca] [-Cx] AGENT changekey [USER]

This command changes the key in a perfect-forward-secrecy compliant way through a diffie-helman exchange.
The remote agent must support the SNMP-USM-DH-OBJECTS-MIB for this command to work. The resulting keys
are printed to the console and may be then set in future command invocations using the
--defAuthLocalizedKey and --defPrivLocalizedKey options or in your snmp.conf file using the
defAuthLocalizedKey and defPrivLocalizedKey keywords.

Note that since these keys are randomly generated based on a diffie helman exchange, they are no longer
derived from a more easily typed password. They are, however, much more secure.

To change from a localized key back to a password, the following variant of the passwd sub-command is
used:

snmpusm [COMMON OPTIONS] <-Ca | -Cx> -Ck AGENT passwd OLD-KEY-OR-PASSPHRASE NEW-KEY-OR-PASSPHRASE
[USER]

Either the -Ca or the -Cx option must be specified. The OLD-KEY-OR-PASSPHRASE and/or NEW-KEY-OR-
PASSPHRASE arguments can either be a passphrase or a localized key starting with "0x", e.g. as printed
out by the changekey sub-command.

Note that snmpusm REQUIRES an argument specifying the agent to query as described in the .I snmpcmd(1)
manual page.

EXAMPLES

       Let's assume for our examples that the following VACM and USM configurations lines were in the snmpd.conf
       file  for  a  Net-SNMP agent.  These lines set up a default user called "initial" with the authentication
       passphrase "setup_passphrase" so that we can perform the initial setup of an agent:

              # VACM configuration entries
              rwuser initial
              # lets add the new user we'll create too:
              rwuser wes
              # USM configuration entries
              createUser initial MD5 setup_passphrase DES

       Note: the "initial"  user's  setup  should  be  removed  after  creating  a  real  user  that  you  grant
       administrative privileges to (like the user "wes" we'll be creating in this example.

       Note: passphrases must be 8 characters minimum in length.

   Create a new user
       snmpusm -v3 -u initial -n "" -l authNoPriv -a MD5 -A setup_passphrase localhost create wes initial

              Creates  a  new  user,  here  named "wes" using the user "initial" to do it.  "wes" is cloned from
              "initial" in the process, so he inherits that user's passphrase ("setup_passphrase").

   Change the user's passphrase
       snmpusm -v 3 -u wes -n "" -l authNoPriv -a MD5  -A  setup_passphrase  localhost  passwd  setup_passphrase
       new_passphrase

              After  creating  the  user "wes" with the same passphrase as the "initial" user, we need to change
              his passphrase for him.  The above command changes it from "setup_passphrase", which was inherited
              from the initial user, to "new_passphrase".

   Test the new user
       snmpget -v 3 -u wes -n "" -l authNoPriv -a MD5 -A new_passphrase localhost sysUpTime.0

              If   the  above  commands  were  successful,  this  command  should  have  properly  performed  an
              authenticated SNMPv3 GET request to the agent.

       Now, go remove the vacm "group" snmpd.conf entry for the "initial" user and you have a valid  user  'wes'
       that you can use for future transactions instead of initial.

WARNING

       Manipulating  the  usmUserTable  using this command can only be done using SNMPv3.  This command will not
       work with the community-based versions, even if they have write access to the table.